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Fix for CVE-2014-0076 backported to 0.9.8 branch

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Fix for the attack described in the paper "Recovering OpenSSL
ECDSA Nonces Using the FLUSH+RELOAD Cache Side-channel Attack"
by Yuval Yarom and Naomi Benger. Details can be obtained from:
http://eprint.iacr.org/2014/140

Thanks to Yuval Yarom and Naomi Benger for discovering this
flaw and to Yuval Yarom for supplying a fix.

Thanks for mancha for backporting the fix to OpenSSL 0.9.8 branch.
This commit is contained in:
mancha 2014-03-27 00:55:08 +00:00 committed by Dr. Stephen Henson
parent a375025e4d
commit fff69a7d8c
4 changed files with 89 additions and 11 deletions
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11
CHANGES
View file

@ -4,6 +4,17 @@
Changes between 0.9.8y and 0.9.8za [xx XXX xxxx]
*) Fix for the attack described in the paper "Recovering OpenSSL
ECDSA Nonces Using the FLUSH+RELOAD Cache Side-channel Attack"
by Yuval Yarom and Naomi Benger. Details can be obtained from:
http://eprint.iacr.org/2014/140
Thanks to Yuval Yarom and Naomi Benger for discovering this
flaw and to Yuval Yarom for supplying a fix (CVE-2014-0076)
[Yuval Yarom and Naomi Benger]
Thanks to mancha for backporting the fix to the 0.9.8 branch.
*) Fix handling of warning-level alerts in SSL23 client mode so they
don't cause client-side termination (eg. on SNI unrecognized_name
warnings). Add client and server support for six additional alerts

11
crypto/bn/bn.h
View file

@ -511,6 +511,8 @@ BIGNUM *BN_mod_inverse(BIGNUM *ret,
BIGNUM *BN_mod_sqrt(BIGNUM *ret,
const BIGNUM *a, const BIGNUM *n,BN_CTX *ctx);
void BN_consttime_swap(BN_ULONG swap, BIGNUM *a, BIGNUM *b, int nwords);
/* Deprecated versions */
#ifndef OPENSSL_NO_DEPRECATED
BIGNUM *BN_generate_prime(BIGNUM *ret,int bits,int safe,
@ -740,11 +742,20 @@ int RAND_pseudo_bytes(unsigned char *buf,int num);
#define bn_fix_top(a) bn_check_top(a)
#define bn_check_size(bn, bits) bn_wcheck_size(bn, ((bits+BN_BITS2-1))/BN_BITS2)
#define bn_wcheck_size(bn, words) \
do { \
const BIGNUM *_bnum2 = (bn); \
assert(words <= (_bnum2)->dmax && words >= (_bnum2)->top); \
} while(0)
#else /* !BN_DEBUG */
#define bn_pollute(a)
#define bn_check_top(a)
#define bn_fix_top(a) bn_correct_top(a)
#define bn_check_size(bn, bits)
#define bn_wcheck_size(bn, words)
#endif

52
crypto/bn/bn_lib.c
View file

@ -824,3 +824,55 @@ int bn_cmp_part_words(const BN_ULONG *a, const BN_ULONG *b,
}
return bn_cmp_words(a,b,cl);
}
/*
* Constant-time conditional swap of a and b.
* a and b are swapped if condition is not 0. The code assumes that at most one bit of condition is set.
* nwords is the number of words to swap. The code assumes that at least nwords are allocated in both a and b,
* and that no more than nwords are used by either a or b.
* a and b cannot be the same number
*/
void BN_consttime_swap(BN_ULONG condition, BIGNUM *a, BIGNUM *b, int nwords)
{
BN_ULONG t;
int i;
bn_wcheck_size(a, nwords);
bn_wcheck_size(b, nwords);
assert(a != b);
assert((condition & (condition - 1)) == 0);
assert(sizeof(BN_ULONG) >= sizeof(int));
condition = ((condition - 1) >> (BN_BITS2 - 1)) - 1;
t = (a->top^b->top) & condition;
a->top ^= t;
b->top ^= t;
#define BN_CONSTTIME_SWAP(ind) \
do { \
t = (a->d[ind] ^ b->d[ind]) & condition; \
a->d[ind] ^= t; \
b->d[ind] ^= t; \
} while (0)
switch (nwords) {
default:
for (i = 10; i < nwords; i++)
BN_CONSTTIME_SWAP(i);
/* Fallthrough */
case 10: BN_CONSTTIME_SWAP(9); /* Fallthrough */
case 9: BN_CONSTTIME_SWAP(8); /* Fallthrough */
case 8: BN_CONSTTIME_SWAP(7); /* Fallthrough */
case 7: BN_CONSTTIME_SWAP(6); /* Fallthrough */
case 6: BN_CONSTTIME_SWAP(5); /* Fallthrough */
case 5: BN_CONSTTIME_SWAP(4); /* Fallthrough */
case 4: BN_CONSTTIME_SWAP(3); /* Fallthrough */
case 3: BN_CONSTTIME_SWAP(2); /* Fallthrough */
case 2: BN_CONSTTIME_SWAP(1); /* Fallthrough */
case 1: BN_CONSTTIME_SWAP(0);
}
#undef BN_CONSTTIME_SWAP
}

26
crypto/ec/ec2_mult.c
View file

@ -208,9 +208,12 @@ static int gf2m_Mxy(const EC_GROUP *group, const BIGNUM *x, const BIGNUM *y, BIG
/* Computes scalar*point and stores the result in r.
* point can not equal r.
* Uses algorithm 2P of
* Uses a modified algorithm 2P of
* Lopex, J. and Dahab, R. "Fast multiplication on elliptic curves over
* GF(2^m) without precomputation".
*
* To protect against side-channel attack the function uses constant time
* swap avoiding conditional branches.
*/
static int ec_GF2m_montgomery_point_multiply(const EC_GROUP *group, EC_POINT *r, const BIGNUM *scalar,
const EC_POINT *point, BN_CTX *ctx)
@ -244,6 +247,11 @@ static int ec_GF2m_montgomery_point_multiply(const EC_GROUP *group, EC_POINT *r,
x2 = &r->X;
z2 = &r->Y;
bn_wexpand(x1, group->field.top);
bn_wexpand(z1, group->field.top);
bn_wexpand(x2, group->field.top);
bn_wexpand(z2, group->field.top);
if (!BN_GF2m_mod_arr(x1, &point->X, group->poly)) goto err; /* x1 = x */
if (!BN_one(z1)) goto err; /* z1 = 1 */
if (!group->meth->field_sqr(group, z2, x1, ctx)) goto err; /* z2 = x1^2 = x^2 */
@ -266,16 +274,12 @@ static int ec_GF2m_montgomery_point_multiply(const EC_GROUP *group, EC_POINT *r,
{
for (; j >= 0; j--)
{
if (scalar->d[i] & mask)
{
if (!gf2m_Madd(group, &point->X, x1, z1, x2, z2, ctx)) goto err;
if (!gf2m_Mdouble(group, x2, z2, ctx)) goto err;
}
else
{
if (!gf2m_Madd(group, &point->X, x2, z2, x1, z1, ctx)) goto err;
if (!gf2m_Mdouble(group, x1, z1, ctx)) goto err;
}
BN_consttime_swap(scalar->d[i] & mask, x1, x2, group->field.top);
BN_consttime_swap(scalar->d[i] & mask, z1, z2, group->field.top);
if (!gf2m_Madd(group, &point->X, x2, z2, x1, z1, ctx)) goto err;
if (!gf2m_Mdouble(group, x1, z1, ctx)) goto err;
BN_consttime_swap(scalar->d[i] & mask, x1, x2, group->field.top);
BN_consttime_swap(scalar->d[i] & mask, z1, z2, group->field.top);
mask >>= 1;
}
j = BN_BITS2 - 1;